In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in pattern miniaturization.
Typically, these miniaturization techniques involve shortening of the wavelength of the exposure light source. Specifically, conventionally, ultraviolet radiation such as g-lines and i-lines had been used, but currently, mass production of semiconductor elements using KrF excimer lasers or ArF excimer lasers has been started. Moreover, F2 excimer lasers, electron beams, EUV (extreme ultraviolet), and X rays, whose wavelengths are shorter than those of the above excimer lasers, are also being examined.
Furthermore, one example of a known pattern forming material capable of forming patterns with very fine dimensions, is a chemically amplified resist including a base component capable of forming a film, and an acid generator component that generates acid by exposure. Such chemically amplified resists include negative resists, in which the alkali solubility decreases by exposure, and positive resists, in which the alkali solubility increases by exposure.
Conventionally, polymers are used as base components of chemically amplified resists. For example, PHS based resins such as polyhydroxystyrene (PHS) and such resins in which a part of the hydroxyl group is protected by an acid dissociable, dissolution inhibiting group, copolymers derived from (meth)acrylic esters, and such resins in which a part of the carboxy group is protected by an acid dissociable, dissolution inhibiting group, and the like are used.
For example, as the negative chemically amplified resists, those including an alkali soluble resin such as PHS, an acid generator component, and a cross-linking agent are typically used. In such a resist, the resin and the cross-linking agent are cross-linked under the action of the acid generated from the acid generator component by exposure, thus converting from an alkali soluble state to an alkali insoluble state.
However, pattern formation using such a pattern forming material involves a problem of roughness on the top surface or the side wall surface of the pattern. For example, roughness on the side wall surface of the resist pattern, namely, line edge roughness (LER), causes distortions around holes in a hole pattern, and non-uniform irregularities in the line width in a line and space pattern, and thus may negatively affect the miniaturization of semiconductor elements.
Such a problem becomes more serious as the pattern dimension gets smaller. Therefore, an object of lithography using electron beams or EUV is to form fine patterns of about several dozens nm, and thus much less roughness than the current pattern roughness is required.
However, a polymer typically used as the base component is as large as several nm in molecular size (mean-square radius per one molecule). In the developing step of pattern formation, dissolving behavior of a resist in a developing solution is normally performed per each molecule unit of the base component, and therefore the further reduction of roughness is very difficult so long as a polymer is used as the base component.
In response to such a problem, a resist using a low molecular material as the base component has been proposed as a material in order to obtain very little roughness. For example, patent references 1 and 2 have proposed a low molecular material containing an alkali soluble group such as a hydroxyl group, in which a part of or all of the alkali soluble group is protected by an acid dissociable, dissolution inhibiting group.
[Patent Reference 1]
Japanese Unexamined Patent Application, First Publication No. 2002-099088 [Patent Reference 2]
Japanese Unexamined Patent Application, First Publication No. 2002-099089